Rapid particle acceleration due to recollimation shocks and turbulent magnetic fields in injected jets with helical magnetic fields

This article has been accepted for publication in MNRAS © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical SocietyOne of the key questions in the study of relativistic jets is how magnetic reconnection occurs and whether it can effectively accelerate electrons in the jet. We performed 3D particle-in-cell (PIC) simulations of a relativistic electron-proton jet of relatively large radius that carries a helical magnetic field. We focused our investigation on the interaction between the jet and the ambient plasma and explore how the helical magnetic field affects the excitation of kinetic instabilities such as the Weibel instability (WI), the kinetic Kelvin-Helmholtz instability (kKHI), and the mushroom instability (MI). In our simulations these kinetic instabilities are indeed excited, and particles are accelerated. At the linear stage we observe recollimation shocks near the centre of the jet. As the electron-proton jet evolves into the deep non-linear stage, the helical magnetic field becomes untangled due to reconnection-like phenomena, and electrons are repeatedly accelerated as they encounter magnetic-reconnection events in the turbulent magnetic field.We appreciate Christoph Kohn's critical reading and fruitful suggestions that improved the contents of this paper. This work is supported by the NASA-NNX12AH06G, NNX13AP-21G, and NNX13AP14G grants. The recent work is also provided by the NASA through Chandra Award Number GO7-18118X (PI: Ming Sun at UAH) issued by the Chandra X-ray Center, which is operated by the SAO for and on behalf of the NASA under contract NAS8-03060. The work of JN and OK has been supported by Narodowe Centrum Nauki through research project DEC2013/10/E/ST9/00662. YM is supported by the ERC Synergy Grant `BlackHoleCam: Imaging the Event Horizon of Black Holes' (Grant No. 610058). The work of ID has been supported by the NUCLEU project. Simulations were performed using Pleiades and Endeavor facilities at NASA Advanced Supercomputing (NAS: s2004), using Comet at The San Diego Supercomputer Center (SDSC), and Bridges at The Pittsburgh Supercomputing Center, which are supported by the NSF.Peer reviewe